grpc: remove unused callInfo field

[arjan-bal]

Remove unused "on RPC commit" callbacks from callInfo. Callers of OnFinish call option type-assert and invoke the closure directly.

RELEASE NOTES: N/A

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.52%. Comparing base (93e31b4) to head (2f860ff).
⚠️ Report is 8 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #9397      +/-   ##
==========================================
+ Coverage   87.47%   87.52%   +0.05%     
==========================================
  Files         425      429       +4     
  Lines       30303    30641     +338     
==========================================
+ Hits        26508    26820     +312     
- Misses       3794     3820      +26     
  Partials        1        1              

Files with missing lines	Coverage Δ
rpc_util.go	87.01% <ø> (-0.05%)	⬇️

... and 47 files with indirect coverage changes

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